Hello!
I just finished the compilation and installation of glibc 2.4
and got the following:
Original instance of package unmerged safely.
* Gentoo's glibc no longer includes mdns.
* If you want mdns, emerge the sys-auth/nss-mdns package.
Regenerating /etc/ld.so.cache...
sys-libs/glibc-2.4

ones. In
theory, it should be possible since you can distinguish them (local
addresses should not be fully qualified _or_ have the domain .local).
net-misc/mDNSResponder, sys-auth/nss-mdns and net-dns/avahi are probably
good starting points.
netdiscover seems to do exactly what the OP asked